Genetic Research Part of Human Descent

The history of modern humans is still a rough draft, under revision.

At one point, genetic studies appeared to offer some resolution to the longstanding debate over how human ancestors spread across the Earth, according to Henry Harpending, a University of Utah anthropology professor.

But more recent evidence has added a plot twist.

Modern humans may not have colonized the Earth like a cloud of locusts?spreading out rapidly?but more like Africanized honey bees?moving outward in waves, he said.

Harpending spoke as part of the Frontiers of Science lecture series in the Skaggs Biology Building Wednesday evening.

The first anatomically modern humans appeared in Africa about 100,000 years ago, and about 65,000 years later, they showed up on other continents.

The question, for 60 years, has been how.

One camp hypothesized a small-population boom carried modern humans across the continents, overrunning the older populations already present.

The other side believed modern humans arose in different regions from existing populations.

In the 1980s, analyses of DNA passed only through the maternal line showed humans descended from a common ancestor about 250,000 years ago?supporting the theory that humans arose from a small population.

In the early ?90s, anthropologists seemed to have all the answers, Harpending said.

But it became apparent that the idea of a sudden boom and expansion in population did not fit.

Instead, the idea of a slow, wave-like spread across the continents seemed to make more sense.

Genetic diversity is low among young populations. After a population has become well established, diversity increases.

Africans show the most genetic diversity among any world population?they are also the oldest. The populations in Europe, Asia and the Americas are progressively less genetically diverse.

Complicating matters, the stories uncovered by anatomists and by archaeologists do not agree.

Though anatomically modern humans showed up 100,000 years ago, physical evidence of the art and technology associated with them did not appear until 45,000 years ago.

But contrary to mainstream thought, Harpending thinks that the clues left behind in the form of weapons, beadwork and cave paintings have little bearing on the story of human dispersion.

Decorations and ?fancy technology? are thought to be signatures of our species, he said.

But he began to question this view, thinking of the Kalahari Bushmen who scratch out a living with simple, unadorned tools.

?Bushmen don?t have any art,? he told The Daily Utah Chronicle. ?You look around the world?where do you see this kind of thing??

The answer, he said, is in societies where men have free time?often at the expense of women?s labor.

American Indian men living along the Northwest coast put in long hours during the salmon season, but the rest of the year, women foraged while the men built totem poles and war canoes, he said.

No trace of the path that led modern humans to Australia 42,000 years ago exists, probably because survival was too difficult to afford them the luxury of art or decorative tools.

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